Is 203 commonly used?

No, it is very rarely used. Most proxies that modify content still return 200 OK.

Should I handle 203 differently from 200?

In most cases, you can treat it the same as 200, but be aware the response may have been altered by an intermediary.

HTTP 203 Non-Authoritative Information — What It Means & How to Fix It

Informational2xx success

Overview

The HTTP 203 Non-Authoritative Information status code indicates the request was successful but the response payload has been modified by a transforming proxy.

Key Details

This status code indicates the response metadata is not exactly the same as what the origin server provided.
It is typically returned by a proxy that has modified the response headers or body.
The original response from the origin server would have been 200 OK.
It is rarely seen in practice and mostly theoretical.

Common Causes

A transforming proxy modified the response content before forwarding it.
A CDN or caching layer altered response headers.
Content adaptation or compression by an intermediary.

Steps

1If you need the original response, bypass the proxy and connect directly to the origin.
2Check proxy and CDN configurations for content transformation rules.
3Compare the response with a direct request to the origin server.
4Review the Via header to identify intermediary servers.